Use custom logic for lambda instead of json path (#154)

crates/air-lib/lambda/ast/Cargo.toml

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+[package]
+name = "air-lambda-ast"
+description = "Parser of AIR value algebra values"
+version = "0.1.0"
+authors = ["Fluence Labs"]
+edition = "2018"
+license = "Apache-2.0"
+publish = false
+keywords = ["fluence", "air", "lambda", "ast"]
+categories = ["wasm"]
+
+[lib]
+name = "air_lambda_ast"
+path = "src/lib.rs"
+
+[dependencies]
+non-empty-vec = { version = "0.2.0", features = ["serde"] }
+
+serde = { version = "1.0.118", features = ["rc", "derive"] }
+serde_json = "1.0.61"

crates/air-lib/lambda/ast/README.md

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+## AIR lambda AST
+
+AIR supports lambda expressions that could be applied both to scalars and streams. This crate defines an AST of such expressions, it has a array-like structure, because such a structure is easier to handle.

crates/air-lib/lambda/ast/src/ast.rs

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+/*
+ * Copyright 2021 Fluence Labs Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+mod traits;
+
+use non_empty_vec::NonEmpty;
+use serde::Deserialize;
+use serde::Serialize;
+
+pub type LambdaAST<'input> = NonEmpty<ValueAccessor<'input>>;
+
+#[derive(Debug, PartialEq, Clone, Copy, Serialize, Deserialize)]
+pub enum ValueAccessor<'input> {
+    // (.)?[$idx]
+    ArrayAccess { idx: u32 },
+
+    // .field
+    FieldAccess { field_name: &'input str },
+
+    // needed to allow parser catch all errors from a lambda expression without stopping
+    // on the very first one. Although, this variant is guaranteed not to be present in a lambda.
+    Error,
+}

crates/air-lib/lambda/ast/src/ast/traits.rs

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+/*
+ * Copyright 2021 Fluence Labs Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+use super::*;
+
+use std::fmt;
+
+impl fmt::Display for ValueAccessor<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use ValueAccessor::*;
+
+        match self {
+            ArrayAccess { idx } => write!(f, ".[{}]", idx),
+            FieldAccess { field_name } => write!(f, ".{}", field_name),
+            Error => write!(f, "a parser error occurred while parsing lambda expression"),
+        }
+    }
+}

crates/air-lib/lambda/ast/src/lib.rs

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+/*
+ * Copyright 2021 Fluence Labs Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#![deny(
+    dead_code,
+    nonstandard_style,
+    unused_imports,
+    unused_mut,
+    unused_variables,
+    unused_unsafe,
+    unreachable_patterns
+)]
+
+mod ast;
+
+pub use ast::*;
+
+pub fn format_ast(lambda_ast: &LambdaAST<'_>) -> String {
+    let mut formatted_ast = String::new();
+    for algebra in lambda_ast.iter() {
+        formatted_ast.push_str(&algebra.to_string());
+    }
+
+    formatted_ast
+}